1. THE DRIER THE BERRY, THE
SWEETER THE JUICE
Jaime Knoch #1303732, Stephanie Black #1302744,
Max Lauch #1304830, Kylee Innes #1308846, Deep
Inamdar #1310484

2. (Anon, 2011)
ABSTRACT
Though both are intended for dessert drinking, wines produced from freezing and from noble rot fungal
infections differ significantly. The two opposing production processes each have similar effects on sugar
concentrations but differing methods of extracting important phenolic compounds, like anthocyanins,
tannins, and flavonoids. Icewine relies on creation of water crystals to dehydrate the grapes and break the
cells while noble rot infections utilize pectolytic enzymes to break the cells and cause dehydration. Despite
vastly different circumstances, one requiring bitter cold temperatures while the other requires a warm, dry
environment; the end products are both characteristically sweet wines.
THE DRIER THE BERRY, THE
SWEETER THE JUICE
Stephanie Black, Deep Inamdar, Kylee Innes, Jaime Knoch, Max Lauch

3. FROZEN AND ROTTED GRAPES
With the national affinity to the sweet taste of
maple syrup, it comes as no surprise that Canada is
paving the way for their very own international
recognition of fine dessert wines. Given the
freezing temperatures and harsh winters, it was a
wonder that temperate European grapes could
even survive, let alone produce wine. Fortunately
for the maple syrup capital of the world, Canada’s
freezing problem became an undeniable asset in
the production of their now-iconic icewines. It
began with the immigration of German
winemakers carrying the tradition of Eiswein
(German icewine) to British Columbia and Ontario
in the 1970’s. The Niagara Region in particular has
almost ideal climate conditions for reliable
production of icewine: warm summers to ripen the
grapes, and cold winters to freeze them (VQA,
2015).
Sub-zero temperatures aren’t the only factor
working against grapes in the Niagara Region. Due
to an environment prone to rainfall and humidity,
winemakers often have to battle the grey rot
fungus, Botrytis cinerea. Winemakers in Eastern
Europe have been utilizing this fungus to produce
their own dessert wines, known as noble rot wines,
for centuries.
Despite vastly different circumstances, one
requiring bitter cold temperatures while the other
requires a warm, dry environment; the end
products are both characteristically sweet dessert
wines. So how do these dissimilar processes result
in similar outcomes? The answers, of course, lie in
the chemical and biological processes that generate
these unique wines.
ICEWINE PRODUCTION
Icewine is classified as a dessert wine due to its
characteristic sweetness, which is a result of its
unique harvesting process. Traditionally, grapes are
harvested immediately after they ripen. This
maintains the desired acidity and sweetness, while
ensuring seeds, skin, and stems are fully developed.
Icewine berries however, are harvested much later
in the season.
The uniquely late harvest can only occur after the
grapes have been properly frozen while on the
vine. According to the Canadian Vintners
Association, proper icewine grapes must be
subjected to temperatures of below -8°C for three
consecutive days before harvest (Canadian
Vintners Association, 2014). On the third day, the
grapes are picked after midnight to avoid an
increase in ambient temperature from solar
radiation (Bell, 2012).
The grapes must remain frozen during production,
so they are immediately pressed that night, often
outside or in unheated cellars. Normally these
grapes would be around 80 percent water, but for
icewines, the water is frozen while the grapes are
pressed (Inniskillin, 2015). In order to force juice
out of the frozen grapes, the hydraulic press
employs much higher pressures than the regular
presses (VQA Ontario, 2015). This effectively
“dehydrates” the juice, as most of its water content
is left behind. Removing this water concentrates
sugars to a final level of at least 35° brix, which is
approximately equivalent to the percentage of
sugar in the wine (Canadian Vintners Association,
2014; VQA, 2015).
However, this high sugar concentration hinders
fermentation, as it creates a hostile environment
for yeast (VQA Ontario, 2015). As a result,
fermentation takes much longer than for other
wines, and the alcohol content tends to be much
lower.
“Temperatures below -8
degrees Celsius for three
consecutive days before
harvest” (Canadian Vintners
Association, 2014)

4. CHEMICAL COMPOSITION OF
ICEWINE
Winemakers are constantly monitoring a number
of factors that enable them to produce their
desired refined product. Icewine makers not only
have to closely monitor temperature, but also berry
exposure to sunlight, soil moisture content, and
total fermentation time, to name a few.
The quality of the final production is assessed
through taste, colour, and aroma. Due to the
qualitative nature of these assessments, there is no
easy quantitative method to determine the end
quality of the wine. However, all these
characteristics (taste, colour, and aroma) are
governed by the concentration of specific
molecules within the wines. In 2004, a study by
Nurgel et al. acknowledged that the key impact
molecules contributing to icewine characteristics
had not yet been identified.
The freezing process does not simply alter the
sweetness of the wine, it also has significant effects
on phenolic compounds (compounds whose
presence is responsible for taste, aroma and
colour) (Vidal et al, 2004). Through cryoextraction
methods, which use artificially frozen grapes, it has
been shown that the formation of ice crystals
physically breaks the lining of grape cells and
organelles, specifically the vacuoles within grape
skin cells. These vacuoles contain phenolic
compounds like tannins (responsible for
astringency and flavour), anthocyanins (a pigment
responsible for colour), and other flavonoids that
give the grapes their unique characteristics (Sacchi,
Bisson and Adams, 2005).
Icewines are unique because the extract from the
pressed frozen berries is highly concentrated with
sugar due to natural freezing. As mentioned
before, during the frozen pressing, much of the
original water content remains in the presses as ice,
while the extract contains highly concentrated
sugars, acids, and phenolic compounds. The sugar
ultimately leads to the signature sweetness of
icewines; however, it also leads to a complication
in fermentation. The elevated sugar content in the
juice creates a hostile environment for the thriving
yeast by having sugar levels exceed those that allow
for sustainable fermentation by the yeast. Thus, the
yeast requires a longer fermentation period of 2-4
weeks, as opposed to the
traditional 1-2 weeks, to
successfully produce an
appropriate amount of
alcohol. Due to the stress
placed on the yeast by the
high sugar and increasing
alcohol concentrations,
alcoholic fermentation
typically ends while there
is still considerable
residual sugar present. As
a result, icewine maintains
a high concentration of
sugars, acids, and
phenolic compounds with
a lower alcohol content.
FIGURE 1: FROZEN GRAPES PRIOR TO HARVEST. These grapes have
frozen on the vine in substantially cold temperatures for three consecutive days, and are
now ready for harvest (Rivard, 2012).

5. NOBLE ROT WINE
PRODUCTION
Even when a winemaker is
cursed with a temperate climate,
they can still produce sweet
dessert wines; they may just
have to get their hands a little
dirty. Botrytis cinerea is a parasitic
fungus that has been involved in
the production of wine for
centuries. Botrytis cinerea can give
rise to two different forms of
fungal development; the
detrimental grey rot (or bunch
rot) and the beneficial noble rot.
Grey-rotted grapes produce
wines that are of extremely low
quality (Jackson, 2008). The
same cannot be said for noble
rotted wines. In fact, noble rot
has been attributed to some of
the world’s finest sweet white
wines such as the acclaimed
Tokaji Aszu, Sauternes, and
Trockenbeeren auslese (Fleet,
1993).
Typically, Botrytis cinerea
infections spread through
spores that originate from the
mycelia of previously diseased,
overwintered fungal tissue.
Infections that initiated on
developing grape clusters may
result in latent infections that
can be reactivated. The fungal
resistance of any given plant
declines during fruit maturity.
This allows for the development
of both latent and novel
infections (Jackson, 2008).
Past the point of infection, the
type of fungal formation
developed is dependent on
several factors. Grey rot
development is promoted by
berry splitting, which typically
occurs in shallow-rooting,
highly humid environments.
These conditions are ideal for
grey rot, as they optimize Botrytis
cinerea parasitism (Ribereau-
Gayon, 1988). Instead, the
formation of Noble rot occurs
later in season and requires
conditions that fluctuate in
humidity. These unique
conditions are ideal, as they
allow for Botrytis cinerea infection
while limiting fungal growth and
metabolism. Botrytis cinerea is
highly sensitive; thus slight
variations in conditions will
heavily affect the yield of
infected grapes (Ribereau-
Gayon, 1988). This is
demonstrated by the variable
expression of healthy, noble-
rotted, and grey-rotted berries
within a single infected grape
cluster. Even microclimates
within infected plants can affect
the formation of the fungus
(Jackson, 2008).
Following the initial infection,
new spores can be produced by
fungal hyphae within the span
of a week. These spores
typically spread the fungus to
unaffected portions of the plant.
Upon infection, several
hydrolytic enzymes are released
into the host plant. Pectolytic
enzymes have the most
noticeable biochemical
effect on plants. As
suggested by the name,
pectolytic enzymes break
down the pectin building
blocks of the plant cell
walls. This degradation
results in a loss of
physiological control:
moisture can freely escape
infected grapes.
During fruit maturation,
this is problematic as
vascular connections with
the vine become
disrupted; plant cells can
no longer replace lost
moisture in order
maintain internal water
FIGURE 2: GRAPES INFECTED WITH NOBLE ROT. Noble rot dehydrates
the grapes and concentrates sugars, producing a sweeter wine (Tosi et al., 2012).

6. levels and are thus subjected to
their environmental conditions.
Under dry environmental
conditions, moisture is lost
form plant, effectively
dehydrating the grape. Grape
dehydration is ideal as it
concentrates the sugar content
while limiting the water
dependent metabolic growth of
noble rot. This ensures that
noble rot does not completely
parasitize its host. Wines
produced from such grapes are
high in quality, having a sugar
content similar to icewines.
(Tosi et al., 2012). If
environmental conditions do
not remain dry, fruit moisture
will be replaced. Dehydration
does not occur and thus the
sugar is not concentrated.
Furthermore, the hydration
allows Botrytis cinerea to grow
and further parasitize the host
fruit until the cell walls collapse
and cellular death occurs
(Jackson, 2008). This presents
an issue for wine makers. Botrytis
cinerea requires moist
environments in order to infect
grapes. However, too moisture
will result in grey rot. Botrytis
cinerea is very difficult to control
as there is a delicate moisture
balance. That being said, wine
growers can implement various
strategies in order to promote
the growth of the noble-rotted
grapes.
When producing noble rot
wine, vineyard locations should
be chosen in order to maximize
sun exposure and control the
humidity conditions that that
allow grey rot to thrive. Wine
growers should grow resistant
varietals that are less susceptible
to grey rot (Rombough 2002). It
is fundamental to utilize
pruning and training systems to
improve air circulation and
promote rapid leaf drying. In
particular, pruning around the
grape cluster will increase air
circulation directly around the
cluster, allowing for dry
microclimates. In the
production of noble rot wines,
it is important to strictly
maintain nitrogen levels; excess
nitrogen promotes tender plant
growth that is more susceptible
to the fungus (Rombough,
2002).
Although some cellular activities
are negatively impacted, the
associated grape dehydration
can be beneficial to the wine
industry. After all, by removing
water, the concentration of the
remaining juice is drastically
increased, leading to a sweeter
and uniquely flavourful wine.
THE CHEMISTRY OF
NOBLE ROT
There are two major types of
chemical changes that occur to
a wine that is produced from
noble-rotted grapes. The most
noticeable change is the sharp
increase in sugar concentration,
but there are also many
chemical effects that occur due
to the metabolic activity of
Botrytis cinerea.
As mentioned previously, the
concentration of juice produced
from noble rot wines is much
higher due to the dehydrating
effect of the fungus. This means
that the resultant wine has
significantly higher sugar
content than wine made from
healthy grapes. Just like the
dehydration from freezing, this
drastically increases the
sweetness of the wine.
There are many interesting
chemical changes in noble-
rotted wine that come about as
a result of the metabolic
processes of the invading fungi.
Thiamine (vitamin B1) and
pyridoxine (vitamin B6) have
been shown to largely decrease
in noble-rotted must (Dittrich et
al., 1975). Botrytis cinerea is also
able to synthesize many
chemical compounds that can
influence the characteristics of
the wine. For instance, it
produces two different groups
of polysaccharides
(carbohydrate chains): pure β -
D-glucan, and a second group
of polysaccharides containing
mannose, galactose, glucose,
and rhamnose (Jackson, 2011).
The β-D-glucan group is
comprised of polysaccharides
containing β -1,3 linkages in the
main chain. These types of
polysaccharides are neutral in
terms of their effect on the
sensory experience of the wine;
however, they tend to form
strand-like colloids in the
alcoholic environment. These
linear strands make filtration of
the wine very difficult because
they plug up the filter sheets
typically used by winemakers
(Jackson, 2011).
The second group of
polysaccharides that B. cinerea
produces was described by
Doubourdieu in 1978, and it
consists of mainly mannose and
galactose, with small amounts of
glucose and rhamnose (Jackson,
2011). They are thought to
bring about the acetic acid and

7. glycerol production from the
yeasts used during fermentation
(Donéche, 1993).
These polysaccharides may also
explain why noble rot wines are
so notoriously difficult to
ferment compared to wines that
are derived from healthy fruit.
They promote a substance once
called “botryticin”, which is
thought to be a mannose-based,
neutral heteropolysaccharide
that acts as an antibiotic during
fermentation (Hornsey, 2007).
Aside from polysaccharide
synthesis, one of the main
chemical differences between
noble rot wines and wines made
from healthy grapes is the
higher concentration of
phenylacetylaldehyde, which is
thought to bring out honey and
ginger notes in the wine
(Jackson, 2011). Other
odourous compounds are also
found in higher concentration
in noble rot wines such as:
benzylaldehyde, vanillin, 4-
terpineol, 1-octen-3-ol, and
sherry lactones, which are
thought to bring about the
aromas of citrus and dried fruits
(Jackson, 2011).
CONCLUSIONS
The international market for
Canadian icewine is credited to
the Inniskillin wineries. The
harvest of icewine grapes at
Inniskillin’s Niagara location has
ranged from December to
February. Due to the
dependence on climate for
icewine production, there are
few regions worldwide that are
suited for its production; this
includes all Canadian
winemaking provinces,
Northern USA wineries, and
some European countries,
primarily Germany.
Noble rot wines, on the other
hand, are difficult to maintain in
the Niagara wine region. Due to
the largely humid and wet
growing season, winemakers
cannot maintain the dry-humid
balance that is required for the
fungus’ benefits. On the other
hand, it is much more viable for
dessert wine production in
California and Eastern
European wine regions.
Similar to proper raisin wines,
icewine and noble rot wines get
their dessert wine certification
from the high sugar
concentration of the final
product. Regardless of sweet
taste, the wine’s characteristics
will depend largely on varietal,
region, and environmental
factors. Of course, after a great
meal, and paired with a fine
dark chocolate or cheese spread,
it’s up to the consumer to
decide whether they want a
wine made from freezing
temperatures or from a fuzzy
fungal infection.
1. Bell, Robert A. Icewines of Canada. [online] Available at: <http://www.winesofcanada.com/icewine_harvest.html>
[Accessed 25 Oct. 2015].
2. Canadian Vintners Association, 2014. Canadian Icewine. [online] Available at:
<http://www.canadianvintners.com/canadas-industry/canadian-wines/canadian-icewine/> [Accessed 10 October
2015].
3. Doneche, B., 1993. In G.H. Fleet, Wine microbiology and biotechnology (2nd ed. pp. 327-351). Chur Harwood Academic
Publishers.
4. Fleet, G.H., 1993. Wine microbiology and biotechnology. CRC Press.
5. Fournier, E., Gladieux, P. and Giraud, T., 2013. The ‘Dr Jekyll and Mr Hyde fungus’: noble rot versus gray mold
symptoms of Botrytis cinerea on grapes. Evolutionary applications, 6(6), pp.960–9. Available at:
<http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=3779096&tool=pmcentrez&rendertype=abstract>
[Accessed 12 Oct. 2015].
6. Hornsey, I., 2007. The Chemistry and Biology of Winemaking. Materials Today.
7. Inniskillin, 2015. World class icewines. [online] Available at:
<http://www.inniskillin.com/index.cfm?method=pages.showPage&PageID=FE4BA9AC-DEB4-843C-74DC-
B26DEC3DFEC0&originalMarketingURL=Niagara/Icewine/Overview> [Accessed 6 October 2015].
8. Jackson, R.S., 2008. Wine science: principles and applications. Academic press.
9. Jackson, R.S., 2011. Speciality Wines. [online] Academic Press. Available at:
<https://books.google.com/books?id=qofTdYZ9HRQC&pgis=1> [Accessed 12 Oct. 2015].
10. Jackson, R.S., 2014. Wine Science: Principles and Applications. [online] Elsevier. Available at:
<https://books.google.com/books?id=Y1cXAwAAQBAJ&pgis=1> [Accessed 12 Oct. 2015].
MORE TO EXPLORE
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8. 11. Nurgel, C., Pickering, G.J. and Inglis, D.L., 2004. Sensory and chemical characteristics of Canadian ice wines. Journal of
the Science of Food and Agriculture, [online] 84(13), pp.1675–1684. Available at: <http://doi.wiley.com/10.1002/jsfa.1860>
[Accessed 11 Jun. 2015].
12. Ribereau-Gayon, P., 1988. Botrytis: advantages and disadvantages for producing quality wines. In: SECOND
INTERNATIONAL COOL CLIMATE VITICULTURE AND OENOLOGY SYMPOSIUM, AUCKLAND, New
Zeland.
13. Rombough, L., 2002. The grape grower: a guide to organic viticulture. Chelsea Green Publishing.
14. Sacchi, K.L., Bisson, L.F. and Adams, D.O., 2005. A Review of the Effect of Winemaking Techniques on Phenolic
Extraction in Red Wines. (May), pp.197–206.
15. Stevenson, T., 1998. The Wine Encyclopedia. Dorling Kindersley.
16. Tosi, E., Fedrizzi, B., Azzolini, M., Finato, F., Simonato, B. and Zapparoli, G., 2012. Effects of noble rot on must
composition and aroma profile of Amarone wine produced by the traditional grape withering protocol. Food
Chemistry, 130(2), pp.370–375.
17. Vidal, S., Francis, L., Noble, A., Kwiatkowski, M., Cheynier, V. and Waters, E., 2004. Taste and mouth-feel properties
of different types of tannin-like polyphenolic compounds and anthocyanins in wine. Analytica Chimica Acta, [online]
513(1), pp.57–65. Available at: <http://linkinghub.elsevier.com/retrieve/pii/S0003267003013461> [Accessed 20 Jul.
2015].
18. VQA Ontario, 2015. Icewine. [online] Available at: <http://www.vqaontario.ca/Wines/Icewine> [Accessed 6 October
2015].
19. File:Vineyard-Waupoos-Ontario.jpg - Wikimedia Commons. [online] Available at:
<https://commons.wikimedia.org/wiki/File:Vineyard-Waupoos-Ontario.jpg> [Accessed 25 Oct. 2015].